The hepatitis C virus (HCV) produces a state of chronic infection in nearly all acutely infected individuals. Approximately 20% of patients with chronic HCV infection (CHC) develop cirrhosis with subsequent liver failure, portal hypertension, ascites, encephalopathy, and bleeding disorders (Alter M., 1992). Long-term follow-up suggests that these estimates may be conservative (Davis G L, 1990); moreover, chronic HCV infection is strongly associated with hepatocellular carcinoma (Tabor E. et al., 1992).
Interferons (IFNs) are glycoproteins produced by the body in response to a viral infection. They inhibit the multiplication of viruses in protected cells. Consisting of a lower molecular weight protein, IFNs are remarkably non specific in their action, i.e. IFN induced by one virus is effective against a broad range of other viruses. They are however species-specific, i.e. IFN produced by one species will only stimulate antiviral activity in cells of the same or a closely related species. IFNs were the first group of cytokines to be exploited for their potential antitumour and antiviral activities.
The three major IFNs are referred to as IFN-alpha, IFN-beta and IFN-gamma. Such main kinds of IFNs were initially classified according to their cells of origin (leukocyte, fibroblast or T cell). However, it became clear that several types might be produced by one cell. Hence leukocyte IFN is now called IFN-alpha, fibroblast IFN is IFN-beta and T cell IFN is IFN-gamma. There is also a fourth type of IFN, lymphoblastoid IFN, produced in the “Namalwa” cell line (derived from Burkitt's lymphoma), which seems to produce a mixture of both leukocyte and fibroblast IFN.
In particular, human fibroblast interferon (IFN-beta) has antiviral activity and can also stimulate natural killer cells against neoplastic cells. It is a polypeptide of about 20,000 Da induced by viruses and double-stranded RNAs. From the nucleotide sequence of the gene for fibroblast interferon, cloned by recombinant DNA technology, Derynk et al. (Derynk R. et al., Nature 285, 542-547, 1980) deduced the complete amino acid sequence of the protein. It is 166 amino acid long.
Shepard et al. (Shepard H. M. et al., Nature, 294, 563-565, 1981) described a mutation at base 842 (Cys→Tyr at position 141) that abolished its anti-viral activity, and a variant clone with a deletion of nucleotides 1119-1121.
Mark et al. (Mark D. F. et al., Proc. Natl. Acad. Sci. U.S.A., 81 (18) 5662-5666, 1984) inserted an artificial mutation by replacing base 469 (T) with (A) causing an amino acid switch from Cys→Ser at position 17. The resulting IFN-beta was reported to be as active as the ‘native’ IFN-β and stable during long-term storage (−70° C.).
Rebif® (recombinant human Interferon-beta-1a) is the latest development in interferon therapy for multiple sclerosis (MS) and represents a significant advance in treatment. Rebif® is Interferon (IFN)-beta-1a, produced from mammalian cell lines.
The mechanisms by which IFNs exert their effects are not completely understood. However, in most cases they act by affecting the induction or transcription of certain genes, thus affecting the immune system. In vitro studies have shown that IFNs are capable of inducing or suppressing about 20 gene products.
There is no completely effective therapy for CHC. The best results have been obtained with interferon-alpha, although this is not a universally-recommended therapy. Many clinicians only observe patients with CHC because of the uncertain natural history of HCV infection and the toxicity associated with interferon-alpha.
Most patients with CHC do not achieve complete responses to treatment with interferon-alpha. Controlled trials of interferon-alpha administered for six months resulted in normalisation of serum ALT in 40 to 50% of patients at the end of treatment, but this response was sustained in only 15 to 25% (Hoofnagle J H et al., 1997).
Dose escalations and increased duration of therapy have resulted in small increases in sustained response, but at the cost of increased expense and toxicity (Poynard T. et al., 1996). In addition, the benefit of higher doses is often transient and relapses are common after therapy has been discontinued (Lindsay K L et al., 1996).
A study of 35 non-responders to interferon-alpha reported no benefit from prolongation of therapy from six to 12 months, increasing the dose of interferon-alpha, switching therapy from recombinant to lymphoblastoid interferon or using steroids (Piccinino F et al., 1993).
The natural history of HCV infection following lack of response to interferon-alpha has not been adequately studied, but in one study follow-up of 28 patients for at least 2 years after therapy found only one case of eventual remission at 16 months (normalisation of ALT and disappearance of HCV RNA) (Takeda T et al., 1993).
Several factors have been found to be associated with greater probability of long-term sustained response to interferon-alpha: non-type 1 genotype, low serum HCV RNA concentration, shorter duration of infection, lower body weight, mild activity on liver biopsy, absence of cirrhosis and low levels of serum ferritin, iron, transferrin saturation and hepatic iron concentration (Schvarcz R et al., 1989, Bacon B R et al., 1995, Conjeevaram H S et al., 1995, Bonkovsky H L et al., 1997).
Patients with CHC who fail to achieve a sustained response after interferon-alpha therapy are thought to have a more aggressive disease course, possibly due to the selection of resistant genotypes, but the development of neutralising antibodies to interferon-alpha may also be a contributing factor. There appears to be a strong correlation between development of neutralising antibodies to interferon-alpha-2a and lack of clinical benefit, in both CHC and hepatitis B virus (HBV) infections (Douglas D D et al., 1993, Milella M M et al., 1993, Lok A S F et al., 1990). In fact, the development of antibodies to a single recombinant type of interferon-alpha may neutralise other Interferon-alpha subtypes (Brand C M et al., 1993).
There is relatively little experience with interferon-beta in HCV infection. Very promising results have been reported for interferon-beta therapy of acute HCV infection, with 7 of 11 patients achieving sustained normalisation of ALT at one year compared to only one of 14 controls (Omata M et al., 1991). The eleven patients were treated for an average of 30 days with a mean IV dose of 52 MU of fibroblast-derived, “native”, and interferon-beta. Notably, no significant toxicity was reported.
Today, in Japan natural IFN-beta is commonly used for the treatment of chronic hepatitis C and the recommended regimen is a daily dose of 3-6 MIU administered i.v. for 6-8 weeks (see Habersetzer et al., Liver, 2000, 20, 438, 4th line).
Very poor clinical efficacy of intramuscular administration of IFN-beta (3 MU t.i.w) in HCV patients of non-Asian race has been shown (Perez R. et al., J. Virol. Hepat. 1995, 2(2), 103-6).
Always in non-Asian (Caucasian) HCV patients subcutaneous administration (9 or 12 MU) of recombinant IFN-beta has shown efficacy at least in a group of patients (Habersetzer et al., Liver, 2000, 20 437-441).
Kishiara et al. (Fukukoka Acta Med., 86(4), 113-20, 1995) disclose a treatment with natural IFN-beta administered i.v. at a dose of 6MIU to HCV patients not responding to IFN-alpha.
In a preliminary comparative study of interferon-alpha vs. interferon-beta in HBV and HCV, response rates were 81% for interferon-alpha and 86% for interferon-beta, with similar response rate maintenance at 6 months (72% for interferon-alpha and 79% for interferon-beta) (Tundo L, 1993). Notably, side effects led to interruption of therapy for 24% of the interferon-alpha group compared to 0% of the interferon-beta group.
The encouraging initial results of some previous studies carried out by the Applicant, along with the good safety and tolerability profile of IFN-beta-1a, led to the design of the study, which explored higher and more intense dose regimens for a longer treatment period in patients with chronic hepatitis C who had failed treatment with IFN-alpha.